First session I was partnered up against a guy who suckered me into a pyramid scheme a while back (I was 17, wanted a summer job), but I didn't have any hard feelings about it, I guess he did because during a thai pad drill (100 knees on one pad while getting punched in the gut with the other) he kept nailing me with low blows.
I told him to keep them up and he just kept doing it, then we get to sparring he goes straight for a kick to the chops, I told him to watch for it, we take a 10 second break, he does it again.
So I threw a jab to the body with the knuckles, speared him pretty good, then one up towards the right side of his face to bring his hands up away from the left side of is body and then I whipped a right hook with the palm down (like how joe louis does in the video, foreman did it in his old age really well too) landing with the top of the pointer knuckle, he made a sound like he was about to puke as he collapsed, was on the ground in the fetal position for 5 minutes after that and then he just left the class.
next two guys I sparred I dropped and dazed with a jab, landing with the pointer and middle knuckle on the chin (dropped) and nose (dazed, said his face went numb)